This idea is original with Phil Goldstein, who published it in The Blue Book of Mentalism, 1976, p. 16, as “The Spirit is Willing (to Write)”. His inspiration was an element in a routine by Elbert L. Gardner, “Glorious Glorpy”, in the Oct. 1973 issue of The Linking Ring. Elbert didn't use the Glorpy gimmick to simulate the animation of a writing implement, but performed the usual ghost-under-the-handkerchief action on top of a pair of spirit slates, which were then separated to reveal a spirit message.
For a detailed history of Glorpy, see “A Brief History of 'It'” by Max Maven in the May 2000 issue of Magic, Vol 9 No. 9, p. 78.
Also see It or The Solid Ghost.